What the heck is a Net Zero Energy Building?

On MNN, I am doing a series about how new smart technologies are going to affect the way we live and work.

Al lot of smart technology is going into making homes net zero energy. I have never really understood this concept, thinking it is better to use less energy than it is to keep adding solar panels and fancy heat pumps until you net out at zero. But it's popular, because it is so well suited to suburbia, like that high tech robotic dinosaur of a NIST House on its vast treeless lot.